1.4 TDI: Is 5th gear at 50 km/h too slow?

Which of the 1.4 TDI drivers has been using the 5th gear for a longer time, especially when only driving at 50 km/h in the city? It's always said that it saves fuel, but I don't think people have ever tried it with that 3-cylinder diesel! It already makes a clacking, ticking, and tacking noise! Or does it work anyway? Does the oil pump build up enough pressure? Who knows a solution?

What is the RPM at 50 km/h in fifth gear?

Best regards, WarLord.

Hi,

I don't think you can save money on gasoline with the 1.4 TDI engine, no matter how you drive.

Sorry, I couldn't resist.

Regarding the question:

According to my information, the 1.4 TDI engine in the Seat Arosa is geared in such a way that it travels at a real speed of 42 km/h at 1000 rpm in 5th gear. I suspect that it might have a shorter gear ratio in larger cars, but I only have the data for the Arosa. At 50 km/h, you would have approximately 1190 revolutions. At a speedometer reading of 50 something, it would likely be somewhere in between, probably around 1100.

You definitely can't damage the engine with that; a diesel engine is designed to handle it. If it vibrates too much, I would probably avoid it for the sake of the bodywork.

It's normal for a diesel engine to sound a bit rough at low RPMs. Additionally, I've observed a kind of "break-in" period with my ASV. At first, I really didn't like the 5th gear at 55 km/h. Today, I can even drive at 45 km/h in the 5th gear without using the accelerator - but you shouldn't accelerate beyond that by gently pressing the gas pedal.

Regarding fuel consumption: My car needs less fuel in 5th gear at 50 km/h after the maintenance (MFA) than it did in 4th gear at the same speed. The difference (although the conditions are never exactly the same) is about 0.2 to 0.4 liters per 100 km.

Best regards,

Jan.

Okay, thank you!
The RPM of my DIESEL is roughly between 1100 and 1200 RPM in 5th gear.
I will then try to drive like that from time to time, and see if a reduction in DIESEL consumption can be noticed!

Hmm, the so-called minimum full-load speed, which VW specifies as being around 1200 RPM, is certainly not completely protected by the engine control unit. The engine maps allow you to operate the engine in a way that causes wear. After all, you can sometimes allow for some wear and tear for a short period. However, I wouldn't recommend flooring the accelerator for extended periods during deep snow conditions.
The reason for this is the piston speed, which is responsible for causing the piston rings to lift and make contact with the oil film. The higher the engine speed, the better the lubrication. At low RPMs with high load, the piston spends a long time at top dead center, resulting in relatively high peak pressures and, consequently, a large amount of blow-by gases that are not beneficial to the oil film.

When measuring the cylinder bore of an old engine, it is often found that the dimension is no longer correct at the top dead center position, specifically at the location of the compression ring.
This is usually the case with defensive drivers! The engine builds compression up until just before Top Dead Center (TDC). At the end of the line, the pressure suddenly drops.

Driving at low RPMs is fine when the engine is under light load. However, if you want to accelerate quickly with a load, it's better to reduce the load and increase the engine speed slightly. Low-speed rumbling = wear and tear. (Even at 4500 rpm...)

Hi,

"Full load," meaning the maximum injection amount, is difficult to achieve below 1200 RPM. The MFA (presumably a data logging system) provides good indications if you know the maximum value for each cylinder. For example, in cylinder 5, the ASV (another system or component) is around 13 liters. I don't think you'll get more than 8 liters at 1000 RPM with full throttle, but I'll try it out tomorrow. If that's correct, then that would be operating at less than 70% capacity...

Normally, in that RPM range, I only accelerate very gently, meaning I only use about a third of the accelerator pedal.

Best regards,

Jan.

Sure, you won't achieve a maximum value... We're still in the process of optimizing the smoke reduction (no turbocharger boost).
'By 'full load', I mean 'pedal to the metal'.'

Hello Martin,

I think Jan and you might have been talking past each other a little.
Jan's statement was intended to explain that even when driving at full throttle (pedal to the metal), it's not possible to generate such high cylinder pressures in the lowest RPM range, as is possible above, for example, 2000 RPM. This is because the turbo boost is simply not present, and the amount of fuel injected is reduced by the engine control unit (ECU).

The load on the crankshaft bearings is primarily determined by the peak combustion pressure, which, under full load, is likely to be only a fraction of the peak pressure observed at higher speeds.
The situation is different for naturally aspirated engines, especially for carburetor-equipped gasoline engines with an accelerator pump. Here, with a heavy foot, it's possible to cause significantly more damage just above idle speed compared to a TDI engine.

Regards,
Alex.

Hi,

I meant exactly what Alex wrote.

I see the load as the ratio of the current chamber pressure to the maximum possible pressure, and the low boost pressure prevents this, for the reasons mentioned above.

It's clear that you can always achieve 100% pedal travel, unless someone puts a doorstop under the pedal.

Best regards,

Jan.

Hi,

Today, I made a few attempts... between 1000 and 1200 RPM, it's difficult to get the average fuel consumption (ASV) in 5th gear above 8 liters per 100 km; it's more likely to be around 6.4. It's difficult to detect because the MFA (presumably a measurement or data) is updated too infrequently, and the speed at which it changes is quite high.

Around 1200, the value then jumps quite abruptly to 10, with a boost pressure of 0.5 bar already present, and with a rapidly increasing tendency.

Perhaps this limit of "1200" can be found somewhere within the software... or, as mentioned before, it might resolve itself through the boost pressure.

Best regards,

Jan.